The ability to accurately and inexpensively genotype single nucleotide polymorphisms (SNPs) is currently limiting for many large-scale association and gene discovery projects. The major hurdle to overcome is cost. This shared instrumentation grant proposes to purchase a new commercial instrument capable of genotyping SNPs for a 20-fold reduction in cost, while maintaining the ability to carry out a high throughput. The technology is base on primer extension and detection with MALDI/TOF mass spectrometry. Simply put, this means that case-control studies and linkage studies which have identified areas of interest and significance from genome wide screens can now test a minimum of 20 times the number of positional and physiological candidate genes with the same NIH supply budget. In the current post-genomic world of all, or nearly all, genes identified in the human genome the progress for the identification of important disease genes such as those causing hypertension or behavioral phenotypes is limited by budgetary constraints. SNP discovery is advancing at a rapid pace as can be observed in the variety of on-line SNP databases. Soon resequencing will provide SNPs for all important genes. This proposal will support eight major NIH funded projects that seek to discover disease genes. Many of these projects will need to test 50 to 100 candidate genes in up to 5,000 human DNA samples. A significant reduction in cost will lead to faster gene discoveries important for medical science.